1. Field of Invention
This application relates to microfluidic devices, and more particularly microfluidic devices that can be used to generate high magnetic field gradients in microfluidic channels.
2. Discussion of Related Art
The contents of all references, including articles, published patent applications and patents referred to anywhere in this specification are hereby incorporated by reference.
Many cell or bio-particle separation or concentration techniques require large electric or magnetic field gradients, such as dielectrophoresis (see, e.g., R. Krupke, F. Hennrich, H. von Lohneysen and M. M. Kappes, Science, 2003, 301(5631), 344-347). Unlike macro-scale devices, high magnetic field gradients in Micro Total Analysis Systems (μTAS) are difficult to generate. Previous developments to generate large magnetic field gradients were achieved by changing the shape and position of magnets that surrounded main fluidic channels. Quadrupole and dipole magnetic systems had been successful for separating cells in channels with diameters in the millimeter range (L. P. Sun, M. Zborowiski, L. R. Moore, and J. J. Chalmers, Cytometry, 1998, 33.4, 469-475; M. Hoyos, L. R. Moore, K. E. McCloskey, S. Margel, M. Zuberi, J. J. Chlamers and M. Zborowski, Journal of Chromatography, 2000, 903, 99-116). The purity of the separated sample is high (99%) but the recovery rate, defined as the percent of target cells recovered from the original sample, is unstable (37-86%) (J. J. Chalmers, M. Zborowski, L. P. Sun and L. Moore, Biotechnology Progress, 1998, 14.1, 141-148). Recent developments use MEMS technology to generate magnetic field gradients through the use of micro-coils and magnetic pillars (Q. Ramadan, V. Samper, D. P. Poenar and C. Yu, Biosensors & bioelectronics, 2006, 21.9, 1693-1702; Q. Ramadan, V. Samper, D. P. Poenar and C. Yu, Biomedical microdevices, 2006, 8.2, 151-158). Although these platforms can easily manipulate the magnetic beads in batches, they do not provide a continuous separation.
The above-mentioned, conventional MEMS magnetic devices require non-trivial and expensive multi-layer fabrication processes in order to integrate the magnetic materials with the microfluidic channels to achieve magnetic-particle separation. Therefore, there is a need for microfluidic devices and systems that have a structure that permits ease of fabrication while still achieving magnetic-based separation.